Tech question regarding C5 Master and electronic distribution
Thread Starter
Le Mans Master
Joined: Aug 2000
Posts: 8,762
Likes: 2
From: Murphy TX
Tech question regarding C5 Master and electronic distribution
All,
I have some questions on the electronic brake pressure proportioning on the C5.
In the old days, master cyllinders had two pistons and the output of each was routed to the front or the rear, or diagonal in order to avoid total brake failure in the event of the failure of a single piston in the m/c.
Now that the C5 (and others) has electronic proportioning, how is the output of each piston in the m/c routed/used? Are they both recombined at the proportioning device (?) ?
So if one piston should fail, how will this be felt? Reduced braking capability? Anything?
Hopefully my question is somewhat clear.
Thanks!
I have some questions on the electronic brake pressure proportioning on the C5.
In the old days, master cyllinders had two pistons and the output of each was routed to the front or the rear, or diagonal in order to avoid total brake failure in the event of the failure of a single piston in the m/c.
Now that the C5 (and others) has electronic proportioning, how is the output of each piston in the m/c routed/used? Are they both recombined at the proportioning device (?) ?
So if one piston should fail, how will this be felt? Reduced braking capability? Anything?
Hopefully my question is somewhat clear.
Thanks!
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,821
From: Charlotte, NC (formerly Endicott, NY)
The dynamic rear proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the mechanical proportioning valve in the base brake system. The DRP control system is part of the operation software in the EBCM. The DRP uses active control with existing ABS in order to regulate the vehicle's rear brake pressure.
In other words the dual brake (front/rear or diagonal) is the same. They do not regulate the pressure using different piston sizes or springs. The ABS controller does the pressure regulation and keeps as much brake pressure on the rear brakes as they can stand without skidding.
If one piston should fail you would get the same reduced braking symptom that you get with a non Dynamic Proportioning brake system.
Bill
In other words the dual brake (front/rear or diagonal) is the same. They do not regulate the pressure using different piston sizes or springs. The ABS controller does the pressure regulation and keeps as much brake pressure on the rear brakes as they can stand without skidding.
If one piston should fail you would get the same reduced braking symptom that you get with a non Dynamic Proportioning brake system.
Bill
Thread Starter
Le Mans Master
Joined: Aug 2000
Posts: 8,762
Likes: 2
From: Murphy TX
Bill, thanks. So if I repeat to ensure I understand - one cyllinder still drives the rear (or diag), but the DRP regulates the pressure supplied to the calipers instead of a spring regulating the m/c piston directly.
If one piston were to fail (or have internal leak-by) I would expect reduced braking capability (dependent on the size of the leak). would this also cause a longer pedal with reduced pressure pushing back on the pedal itself?
I'm fighting what can best be described as a wierd (
) brake pedal. I've bled like crazy and the pedal is hard as a rock with power off, but with power on it takes very little pressure over a large % of its travel - i.e. for a large amount of travel it seems to take constand pressure, not increasing as expected (or increasing slightly). I've done all the standard things (no pad taper, no external leaks, good fresh fluid etc.). This weekend on track it seemed to worsen, and at times I was sure I felt it sinking a little bit with constant pressure.
I'm wondering about the m/c for two reasons - I've done everything else other than an ABS bleed with a TechII, and once, before I knew what I was doing, I did a bleed pushing the pedal all the way to the floor... so am wondering if I scored one of the pistons slightly, causing a minor problem then that is slowly worsening.
Thanks for your comments.
If one piston were to fail (or have internal leak-by) I would expect reduced braking capability (dependent on the size of the leak). would this also cause a longer pedal with reduced pressure pushing back on the pedal itself?
I'm fighting what can best be described as a wierd (
) brake pedal. I've bled like crazy and the pedal is hard as a rock with power off, but with power on it takes very little pressure over a large % of its travel - i.e. for a large amount of travel it seems to take constand pressure, not increasing as expected (or increasing slightly). I've done all the standard things (no pad taper, no external leaks, good fresh fluid etc.). This weekend on track it seemed to worsen, and at times I was sure I felt it sinking a little bit with constant pressure.I'm wondering about the m/c for two reasons - I've done everything else other than an ABS bleed with a TechII, and once, before I knew what I was doing, I did a bleed pushing the pedal all the way to the floor... so am wondering if I scored one of the pistons slightly, causing a minor problem then that is slowly worsening.
Thanks for your comments.
Last edited by yellow01; Sep 13, 2006 at 10:30 AM.
